In crash detection circuits used for the detection of a crash of a vehicle, optocoupler units are often arranged between a crash signal generation circuit and a crash signal evaluation circuit. The aforementioned optocoupler units serve to galvanically isolate the crash signal generation circuit of the vehicle from the electronics of the crash signal evaluation circuit of the vehicle. However, such approaches for crash detection, which are based on optocoupler units, are often relatively expensive, lack sufficient robustness, have a relatively short lifetime, and do not allow for transmittance of differentiated (e.g., positive and negative) signals, as signaling between the crash signal generation circuit and the crash signal evaluation circuit is solely performed via light pulses.
A crash detection circuit of the state of the art may suitably fulfill a plurality of conditions. According to a first condition (e.g., according to a so called no-fire condition), the crash detection circuit shall not detect a crash when a current in the crash signal generation circuit is smaller than or equal to about 0.4 A, and when a current impulse given in the crash signal generation circuit is less than or equal to about 5 A and has a duration that is less than or equal to about 4 μs.
According to a second condition (e.g., according to a so called fire condition), the crash detection circuit shall detect a crash when a current in the crash signal generation circuit is greater than or equal to about 1.75 A and less than or equal to about 40 A for a maximum duration of about 0.5 ms in an operating temperature range and when, for a duration that is less than or equal to 2 ms, a current given in the crash signal generation circuit is greater than or equal to about 1.2 A and has a duration that is less than or equal to about 4 μs.
In FIG. 1, the fire condition and the non-fire condition are illustrated in a coordinate system. The ordinate (e.g., the y-axis) of the coordinate system shows the current given within the crash signal generation circuit, and the abscissa (e.g., the x-axis) of the coordinate system shows the duration for which the respective current is given within the crash signal generation circuit. In FIG. 1, the dark areas illustrate an area in which the fire condition is fulfilled, and the bright areas illustrate an area in which the non-fire condition is fulfilled.